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United States Patent |
6,042,804
|
Huckins
|
March 28, 2000
|
Method for producing hydrogen peroxide from hydrogen and oxygen
Abstract
The invention relates to a method and apparatus for safely producing
hydrogen peroxide by injecting dispersed minute bubbles of hydrogen and
oxygen into a rapidly flowing liquid medium. The minute bubbles are
surrounded by the liquid medium of sufficient volume for preventing an
explosive reaction between the hydrogen and oxygen. The liquid medium is
formed of an acidic aqueous solution and a Group VIII metal catalyst.
Hydrogen is sparged into the flowing medium for dissolution of the
hydrogen in the medium. Oxygen bubbles are reacted with the dissolved
hydrogen for producing hydrogen peroxide. Preferably, the liquid medium
has a velocity of at least 10 feet per second for providing a bubbly flow
regime in the reactor. The invention allows the direct combination of
oxygen and hydrogen while preventing propagation of an explosive condition
within the reactor. The method and apparatus provide for the safe
production of hydrogen peroxide with low manufacturing costs.
Inventors:
|
Huckins; Harold A. (Hilton Head, SC)
|
Assignee:
|
Advanced Peroxide Technology, Inc. (Hilton Head Island, SC)
|
Appl. No.:
|
783881 |
Filed:
|
January 16, 1997 |
Current U.S. Class: |
423/584 |
Intern'l Class: |
C01B 015/01 |
Field of Search: |
423/584
|
References Cited
U.S. Patent Documents
5194242 | Mar., 1993 | Paoli | 423/584.
|
Primary Examiner: Langel; Wayne
Attorney, Agent or Firm: Whitman Breed Abbott & Morgan LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. patent application Ser.
No. 08/509,841, filed Aug. 1, 1995, U.S. Pat. No. 5,641,467, which is a
continuation-in-part of U.S. patent application Ser. No. 08/291,437, filed
Aug. 16, 1994, abandoned.
Claims
What is claimed is:
1. A process for preparing hydrogen peroxide by reaction of hydrogen and
oxygen in the presence of a catalyst, comprising the steps of:
(a) establishing a continuous flow of aqueous reaction medium containing
finely divided catalyst for the said reaction in an elongated reaction
zone;
(b) sparging from one to twenty moles of oxygen and one mole of hydrogen
into said continuously flowing aqueous medium, said hydrogen and oxygen
being sparged at points distanced from one another along the path of said
continuous flow and thereby forming dispersed tiny bubbles of hydrogen and
oxygen, respectively, in said aqueous medium;
(c) maintaining
(i) the volumetric ratio of the flow of said aqueous medium to the
aggregate flow of said gaseous hydrogen and oxygen at from 25 to 300;
(ii) the linear flow rate of aqueous medium at at least 10 feet per second;
and
(iii) the reaction pressure at at least 1200 p.s.i;
(d) after reaction has taken place, introducing the reaction medium into a
gas-liquid separator and therein separating unreacted gases from aqueous
reaction medium containing hydrogen peroxide; and
(e) recovering hydrogen peroxide from said aqueous medium.
2. A process for preparing hydrogen peroxide by reaction of hydrogen and
oxygen in the presence of a catalyst, under conditions at which the
process will not become explosive, comprising the steps of:
(a) establishing a continuous flow of aqueous reaction medium containing
finely divided catalyst for the said reaction in an elongated reaction
zone;
(b) sparging from one to twenty moles of oxygen and one mole of hydrogen
into said continuously flowing aqueous medium, said hydrogen and oxygen
being sparged at points distanced from one another along the path of said
continuous flow and thereby forming dispersed tiny bubbles of hydrogen and
oxygen, respectively, in said aqueous medium;
(c) maintaining
(i) the linear flow rate of aqueous medium at at least 10 feet per second;
(ii) the ratio of the flow of said aqueous medium to the aggregate flow of
said gaseous hydrogen and oxygen at at least 25; and
(iii) the reaction pressure, said conditions recited in (i), (ii) and (iii)
being maintained at levels above those at which the process may become
explosive;
(d) introducing the said reaction medium into a gas-liquid separator and
therein separating unreacted gases from the aqueous reaction medium
containing hydrogen peroxide; and
(e) recovering hydrogen peroxide from said aqueous medium.
3. The process of claim 2, wherein air is added to said unreacted gases
separated from said aqueous reaction medium thereby rendering them inert.
4. The process of claim 2, further comprising the step of substantially
continuously cooling said reaction.
5. The process of claim 2, wherein said pressure is from 1500 p.s.i. to
5000 p.s.i.
6. The process of claim 2, further comprising the step of repeating said
steps of injecting hydrogen gas and injecting oxygen gas into said medium
at multiple points in said elongated reaction zone.
7. The process of claim 2, wherein said hydrogen bubbles have a diameter of
a size which is small enough to be surrounded and quenched by said rapidly
flowing medium.
8. The process of claim 2, wherein said aqueous medium is acidic.
9. The process of claim 8, wherein the acidic medium has a pH of from 1 to
3.
10. The process of claim 2, wherein the reaction takes place in the
flammable range, the volume ratios of oxygen to hydrogen being from 1:1 to
20:1.
11. The process of claim 2, wherein more than 75% of the hydrogen is
reacted in the elongated reaction zone before residual hydrogen is vented
to the atmosphere.
12. The process of claim 2, wherein the hydrogen is introduced first.
13. The process of claim 2, wherein oxygen is introduced after the hydrogen
has become distributed throughout the aqueous medium as fine bubbles and
has substantially dissolved therein.
14. The process of claim 2, wherein a second volume of hydrogen is
introduced after at least 50% of the hydrogen passing the previous point
of oxygen introduction has been reacted.
15. The process of claim 2, wherein the velocity of the aqueous medium is
greater than 15 ft/sec.
16. The process of claim 2, wherein the reaction is carried out
continuously.
17. The process of claim 2, wherein the reaction is carried out in a batch
semicontinuous manner.
18. The process of claim 2, wherein the reactor is composed of elongated
pipes in vertical orientation.
19. The process of claim 2, wherein gases vented from the effluent of the
reactor are recycled to said reactor at a position upstream of the first
hydrogen inlet and wherein said first hydrogen inlet is positioned
upstream of the first oxygen inlet.
20. The process of claim 2, wherein said reaction is continuously cooled.
21. The process of claim 2, wherein said unreacted gases are inerted by the
addition of air.
22. A process for preparing hydrogen peroxide by reaction of hydrogen and
oxygen in the presence of a catalyst, under conditions which are not
explosive, comprising the steps of:
(a) establishing a continuous flow of aqueous reaction medium containing
finely divided catalyst for the said reaction in an elongated reaction
zone;
(b) sparging from one to twenty moles of oxygen and one mole of hydrogen
into said continuously flowing aqueous medium, said hydrogen and oxygen
being sparged at points distanced from one another along the path of said
continuous flow and thereby forming dispersed tiny bubbles of hydrogen and
oxygen, respectively, in said aqueous medium;
(c) maintaining
(i) the volumetric ratio of the flow of said aqueous medium to the
aggregate flow of said gaseous hydrogen and oxygen at from 25 to 300;
(ii) the linear flow rate of aqueous medium at least 10 feet per second;
and
(iii) the reaction pressure; at levels above that at which the process may
become explosive;
(d) introducing the reaction medium into a gas-liquid separator and therein
separating unreacted gases from aqueous reaction medium containing
hydrogen peroxide; and
(e) recovering hydrogen peroxide from said aqueous medium.
23. The process of claim 22, wherein said ratio of the flow of said aqueous
medium to the aggregate flow of said gaseous hydrogen and oxygen is at
least 25.
24. The process of claim 22, wherein said pressure is at least 1200 p.s.i.
25. The process of claim 22, wherein said pressure is from 1500 p.s.i. to
5000 p.s.i.
26. The process of claim 22, wherein the reaction takes place in the
flammable range, the volume ratios of oxygen to hydrogen being from 1:1 to
20:1.
27. The process of claim 22, wherein the velocity of the aqueous medium is
greater than 15 ft/sec.
28. The process of claim 22, wherein the reactor is composed of elongated
reaction zones in vertical orientation.
29. The process of claim 22, wherein said reaction is continuously cooled.
30. The process of claim 22, wherein said unreacted gases are inerted by
the addition of air.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for producing
hydrogen peroxide by injecting minute bubbles of hydrogen and oxygen into
a liquid stream of an aqueous solution of water and an inorganic acid and
a Group VIII metal catalyst in which the liquid stream flows at high
velocity.
2. Description of the Related Art
It is known that a mixture of gaseous oxygen and gaseous hydrogen forms an
explosive material. Virtually all currently produced hydrogen peroxide is
produced by indirectly combining hydrogen and oxygen. Thus, the primary
conventional industrial method for production of hydrogen peroxide uses a
chemical agent first for the reduction or hydrogenation. Typically,
alkylanthraquinone, such as ethyl or tertiary butyl anthraquinone, is used
as the chemical agent. This working solution contains organic solvents
such as di-isobutylcarbinol and methyl naphthalene. Oxidation of the
intermediate product of the reduction reaction produces hydrogen peroxide
and the original alkylanthraquinone. The anthraquinone is recycled back
through the process. This method has the shortcoming that there is a
considerable loss of the anthraquinone and the organic solvents from
oxidation and thermal degradation of these organic materials. The presence
of these organics with oxygen and hydrogen peroxide presents safety
hazards from their potential reactions. This destruction of organics
involves high operating losses for the currently practiced commercial
process.
Various methods have been attempted to directly combine oxygen and hydrogen
to overcome the above-described problems. The direct combination of
hydrogen and oxygen to form hydrogen peroxide has the advantage of not
requiring the use of any organic or combustible materials. The direct
process, however, does require careful control of the gaseous mixture of
oxygen and hydrogen so that they are always outside the explosive range.
There have been numerous patents issued for the direct combination of
hydrogen and oxygen to produce hydrogen peroxide. U.S. Pat. Nos. 4,347,23
and 4,336,240 employ a two phase system through the use of organic
compounds to form a second phase. However, the organics can react with
oxygen or hydrogen peroxide to render these processes uneconomical.
Other patents employ a fixed bed catalyst within a reaction vessel which
has low conversion per pass or low reactor productivity (see for example,
U.S. Pat. Nos. 4,336,239 and 5,082,647).
U.S. Pat. No. 5,169,618 ('618 patent) to Marischino describes establishing
a pulse-flow regime in a catalyst bed. The '618 patent has the limitation
of low conversion of hydrogen peroxide per pass and high equipment costs.
U.S. Pat. No. 4,996,039 describes first absorbing hydrogen into the aqueous
reaction mixture with a catalyst; dropping the pressure to remove all the
hydrogen in the gas phase; and then introducing the oxygen in order to
produce hydrogen peroxide. This technique minimizes the presence of
hydrogen in the gaseous phase. This process is expensive to repressure the
reactor with oxygen and doesn't lend itself to continuous processing.
Continuous modes of operation for the direct combination process have also
been proposed, as disclosed in U.S. Pat. Nos. 4,009,252; 4,279,883;
4,681,751; and 4,772,458. These patents employ a catalyst as a slurry in
an agitated reactor. These patents have the drawback of having either low
conversion per pass or low volumetric efficiency either of which is
uneconomical.
U.S. Pat. No. 4,661,337 ('337 patent) describes a process for direct
combination for producing hydrogen peroxide of increased concentration.
The volume of the reaction mixture occupies a small portion of the
available volume of the reactor. It is taught in the '337 patent that the
layer of reaction mixture has a thickness of no more that 2 millimeters.
This patent has the disadvantage that the majority of the reactor is in
the gas phase in which no hydrogen peroxide is formed.
In all the above described patents, there is a separate continuous gaseous
phase in which it is necessary to inject an inert gas such as nitrogen,
argon or helium in order to remain outside the explosive range of hydrogen
and oxygen.
Other attempts for the direct formulation of hydrogen peroxide use liquid
filled reactors without a continuous gas phase. U.S. Pat. No. 5,104,635
describes a liquid filled reactor with two internal membranes which each
are permeable only for hydrogen and oxygen, respectively. This reaction
system requires considerable capital for the use of the membranes.
U.S. Pat. No. 4,279,883 describes a process for preparing hydrogen peroxide
in an aqueous medium. The aqueous medium contains dissolved hydrogen and a
platinum-group catalyst having absorbed thereto hydrogen. Inert nitrogen
and argon are blown into the aqueous medium so that no dissolved oxygen is
present in the aqueous medium during the hydrogen absorbing treatment.
Oxygen gas is injected into the medium after the absorption of the
hydrogen on the catalyst and the gaseous zone and liquid zones are
stirred. This patent has the shortcoming of requiring an injection of an
inert gas into the reactor during the hydrogen absorption phase to prevent
an explosion between the hydrogen and oxygen gases.
U.S. Pat. No. 5,194,242 ('242 patent) describes a process for preparing
hydrogen peroxide in which an acidic aqueous solution fills an elongated
reaction zone in a tubular reactor. A catalyst is provided to the reaction
zone. Oxygen together with recycled gas and then hydrogen are dispersed
into the solution in proportions that are above the lower flammability
limit for hydrogen and oxygen and are maintained at a temperature and
pressure until the reaction mixture has decreased to below the lower
flammability limit for the hydrogen and oxygen mixture. The partial
pressure of hydrogen and oxygen is super-atmospheric in the range of about
20 to about 400 psi. The aqueous solution flows through the reactor at
liquid velocity at rate from about 4 to about 18 ft/sec.
In the '242 patent, the ratio of the flow of the aqueous medium to the
aggregate flow of the hydrogen and oxygen is such that a gas phase regime
of large elongated bubbles may be produced, which, if reacted violently
would not be surrounded by sufficient liquid volume to cool the gas
mixture, resulting in elevated temperature and pressure which can result
in an explosion of the gas mixture. Patentees provide no teaching of the
importance of operating in a regime in which small discrete individual
bubbles exist which can be quenched by the surrounding medium. It is
desirable to provide a safe direct combination process for producing
hydrogen peroxide which has low manufacturing costs.
OBJECTS OF THE INVENTION
It is a primary object of the invention to provide a process for the
reaction of oxygen and hydrogen which is efficient and safe.
It is a further related object of the invention to provide a process which
operates in the flammable range of oxygen/hydrogen mixtures so as to
benefit from increased reaction rate, without sacrificing the safety
aspects of the process.
It is a further and related object of the invention to increase the molar
ratio of gas (hydrogen and oxygen) relative to aqueous reaction solution
in order to improve the space-time yield of the reactor system but without
jeopardizing the safety of the reactor operation.
It is still a further related object of the invention to substantially
completely react hydrogen during the process in order to maximize the
efficiency of utilization of that expensive reactant.
It is still a further object of the invention to carry out the process with
minute bubbles of hydrogen and oxygen supplied to the reaction zone at a
rate and in such a way as to obviate the risk of explosion.
SUMMARY OF THE INVENTION
The invention comprises a method and apparatus for producing hydrogen
peroxide in which hydrogen and oxygen are separately injected into a
liquid filled reactor to form a plurality of discrete individual bubbles
in a continuous rapidly flowing liquid stream. Each bubble is surrounded
by a continuous liquid phase such that if the hydrogen and oxygen gas
reacted, there is sufficient liquid available to quench/cool down the
reaction in order to prevent an explosion propagating throughout the
reactor. It has been found that it is critical to maintain the ratio of
the volume of flow of aqueous medium to the aggregate volume of flow of
hydrogen and oxygen, at a high value so as to avoid uncontrolled reaction
of hydrogen and oxygen bubbles to form water. By controlling the ratio of
the volume of flow of aqueous medium to the volume of flow of hydrogen and
oxygen, both independently, and, in the aggregate, there is sufficient
liquid volume present to quench any runaway reaction that might take
place. It is also important to maintain the flow velocity of aqueous
medium at at least ten feet per second to obtain a dispersed bubbly flow
regime.
It has been found that the reaction can be safely and efficiently operated
at higher levels of space-time yield if the reaction pressure is above
1200 psi. Preferably, the pressure is above 1500 psi. Most advantageously,
it is from 2000 to 5000 psi.
Preferably, a pipeline reactor is used having a plurality of passes within
the reactor. The pipeline reactor can be formed of a plurality of tubes
arranged vertically or horizontally and connected with curved tubes
(elbows). The liquid stream can be formed of water, a dilute acid and a
Group VIII metal catalyst. The Group VIII metal catalyst can be platinum
or palladium or a mixture of the two on an inert support such as alumina,
silica or carbon. The liquid stream fills the reactor. Recycle gas
containing hydrogen and oxygen is first injected into the flowing liquid
stream. Fine dispersed hydrogen gas bubbles can then be dissolved into the
flowing liquid stream. After the hydrogen is dissolved, finely dispersed
oxygen gas bubbles are injected into the liquid stream for reacting with
hydrogen to form hydrogen peroxide. After this first reaction is complete,
multiple injections of first hydrogen and then oxygen can be used to raise
the concentration of hydrogen peroxide produced to a predetermined level.
The number of injections of hydrogen and oxygen bubbles can be varied for
producing the desired concentration of the hydrogen peroxide.
It has also been found that the safety of the reaction system can be
ensured if the reaction zone is comprised of vertically oriented pipes.
The vertically oriented pipes prevent accumulation of gas bubbles at the
top of horizontally oriented pipes that are very close or touching each
other. If a reaction should occur within these bubbles, there is very
little liquid around each bubble to permit cooling the bubbles. This could
lead to an uncontrolled temperature rise with possible explosive results.
Gas bubbles could also rise in vertical pipes, but the selected liquid
velocity is sufficiently high so that the bubbles move continuously
forward with flowing liquid medium.
It has also been found that it is advantageous to continuously cool the
entire reaction zone throughout the duration of the reaction. In still a
further improvement, it has been found that the step of separating
unreacted gases from the aqueous reaction medium can be carried out by
introducing air into the unreacted gases, rather than nitrogen, and
thereby achieving greater economies of operation.
The present invention has the advantage of avoiding a continuous gas phase
between the hydrogen and oxygen and having full utilization of the entire
volume of the reactor. The production of hydrogen peroxide occurs in the
liquid phase between the dissolved hydrogen gas and oxygen in the presence
of a catalyst. The method prevents an explosive reaction from expanding,
thereby allowing the concentration of unreacted hydrogen and oxygen to be
within the explosive range.
The invention will be more fully described by reference to the following
drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of an apparatus for continuously producing
hydrogen peroxide from hydrogen and oxygen according to an embodiment of
the invention.
FIG. 2 is a schematic diagram of an apparatus for producing hydrogen
peroxide in a semicontinuous batch process according to a second
embodiment of the invention.
FIG. 3 is a schematic diagram of an apparatus for continuously producing
hydrogen peroxide from hydrogen and oxygen according to a third embodiment
of the invention.
FIG. 4 is a schematic diagram of an apparatus for producing hydrogen
peroxide in a semicontinuous batch process according to a fourth
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a schematic view of the apparatus 10 for producing
hydrogen peroxide from hydrogen and oxygen. Water 12 and catalyst 14 are
added to tank 16. Catalyst 14 is preferably a supported Group VIII metal
catalyst. Preferably, catalyst 14 is palladium or platinum or mixtures
thereof. Examples of a support useful for supporting the catalyst in a
dispersed fashion are carbon, silica and alumina. It will be appreciated
that other catalysts known in the art of hydrogen peroxide production can
be used in the present invention.
Preferably, an amount of hydrogen peroxide stabilizer 15 is added to tank
16. Stabilizer 15 can be an acidic solution having a pH in the range of
about 1 to 7, preferably in the range of 1-3. Examples of acids useful for
the present invention are hydrochloric, phosphoric, hydrobromic and other
commercially available inorganic acids. Typically, the amount of
stabilizer 15 added to water is less than about 1% of the reaction medium.
Solution 17 within tank 16 can be stirred with an automatic or manual
agitation means 18.
Solution stream 20 is circulated with recirculating pump 22 as input stream
24. Liquid stream 24 is received at pipeline reactor 26 and fills pipes 27
of pipeline reactor 26. Liquid stream 24 has a flow velocity of greater
than 10 feet per second for avoiding the presence of a continuous gas
phase or elongated bubbles within reactor 26. It is known that dispersed
bubble regime occurs when water has a velocity of greater that 10 feet per
second. "The Flow of Complex Mixtures of Pipes." G. W. Govier, Robert
Kreiger Publishing Company, Malaber, Fla., page 523. Preferably, the flow
velocity of liquid stream 24 is in the range of more than 10 feet per
second to about 50 feet per second. Most preferably, the flow velocity of
liquid stream 24 is in the range of about 11 to about 20 feet per second.
At higher velocities the pressure drop through the pipe becomes too great
and catalyst is lost through attrition.
Pipeline reactor 26 is preferably formed of a plurality of pipes 27 joined
with a 180.degree. bend. Joined pipes 27 can be arranged either vertically
or horizontally. It has been found that significant advantages are
achieved where the reactor pipes are vertically oriented. This avoids
accumulation of gas bubbles in the area at the top of horizontally
oriented pipes. The gas bubbles remain uniformly distributed in a vertical
pipe, each surrounded by enough liquid to be cooled as the reaction
occurs. Use of vertical pipes also avoids the necessity of installing
baffling within horizontal pipes to keep the gas liquid mixture fully
mixed.
The length and diameter 27 of pipes are predetermined for providing the
desired flow velocity. Preferably, pipes 27 are formed of a commercially
available heavy wall pipe such as a U.S. schedule 80 or 160 which has a
wall thickness from 0.147 to 1.125 inches over the size range of 1/2 to 10
inches. Pipes 27 useful for practice of the invention can have diameters
in the range of 1/2 inch to at least 10 inches. The preferred length of
pipeline reactor 26 can vary widely depending on the number of joined
pipes 27 used in the reactor. Typically, joined pipes 27 have a total
length in the range of about 50 to about 60,000 feet. Preferably, joined
pipes 27 have a length of about 1,000 to about 20,000 feet.
It will be appreciated that the number of pipes 27 used in pipeline reactor
26 can be varied to change the number of injection points or passes in the
pipeline reactor 26. Preferably, the number of passes of pipeline reactor
26 is between about six and about 48 passes.
The pipeline reactor 26 operates at a pressure in the range of about
between 30 to about 300 atm. The pressure is desirably above 1200 psi
(approximately 80 atm.), preferably is above 1500 psi and most
advantageously is in the range of 2000 to 5000 psi. Another advantage of
higher pressure is that the higher the pressure, the greater the
solubility of hydrogen in solution.
The reaction temperature normally is in the range of 0.degree. C. to
60.degree. C. The lower the temperature of the aqueous medium the higher
the solubility of hydrogen is in solution. The reaction temperature can be
maintained by providing jacketing on each pipe 27 or by installing the
entire pipeline reactor 26 within a vessel in which a refrigerant is being
evaporated or cold liquid solution is circulated. It has been found that
best results can be obtained if the entire pipeline reactor is
substantially continuously cooled during operation.
It has been found that it is critical to maintain the ratio of the
volumetric flows of the aqueous reaction medium and the aggregate flows of
the gaseous hydrogen and oxygen at a level which ensures that the system
remains within the bubbly flow regime. The choice of volumetric flow ratio
is within the skill of the reactor operator. Advantages in productivity
are achieved by operating at lower L/G ratios. However, where that ratio
is too low, the system will not be in a dispersed bubbly flow regime,
leading to the possibility of an explosive condition occurring. By
increasing the reaction system pressure, it is possible to produce more
hydrogen peroxide per unit time in a reactor of given volume. If the flow
ratios are maintained within the range of 300-25, and desirably at the
lower end of that range, and the velocity of the flowing liquid is
maintained at above 10 feet per second, as described above, a regime of
tiny bubbles is surrounded by adequate aqueous medium. This assures that
the bubbles never overheat and/or coalesce leading to the risk of runaway
explosion. Statistically, the local increase of the temperature due to the
reaction of hydrogen and oxygen bubbles to form water is desirably less
than 3.degree. C. This is achieved with the volumetric flow rates and
velocities of the invention.
A gaseous stream of hydrogen 28 is injected by valve 30 into a flowing
liquid stream 24 at point 31. Liquid stream 24 flows between points 31 and
33 of pipe 27. Hydrogen is dissolved in a liquid stream 24. A gaseous
stream of oxygen 34 is injected by valve 32 into liquid stream 24 at point
33. Within pipeline reactor 26, the dissolved hydrogen 28 reacts with the
gaseous oxygen 34 to form hydrogen peroxide in solution.
Preferably, gaseous hydrogen 28 and gaseous oxygen 34 are sparged into
liquid stream 24 by a small diameter nozzle for producing a plurality of
minute bubbles. Preferably, the nozzle has a diameter in the range of
about 0.01 inches to about 0.50 inches to produce fine bubbles which are
surrounded by rapidly flowing liquid stream 24. The minute bubbles of
hydrogen and oxygen are of a size which is small enough to be surrounded
by flowing liquid stream 24. The volume of liquid stream is sufficiently
large and continuous so that in the event of any explosion of a single
bubble the surrounding liquid can expeditiously quench the explosion
within the bubble to prevent the propagation of the explosion throughout
the entire regime of the reactor. The flow rate of liquid stream 24 and
the injection of minute bubbles provide a dispersed bubbly regime in
liquid stream 24.
Additional gaseous hydrogen 28 can be injected at a plurality of passes
through pipeline reactor 26 with respective valves 35, 46, 50, 55 and 59
at points 36, 47, 51, 56 and 60 for dissolution into liquid stream 24.
Additional gaseous oxygen 34 can be injected downstream of hydrogen
injection points 36, 47, 51, 56 and 60 with respective valves 40, 48, 53,
57 and 61 at respective points 41, 49, 54, 58 and 62 for reacting with the
dissolved hydrogen.
Desirably, the point of oxygen introduction is sufficiently distanced from
that of hydrogen injection to permit the hydrogen to have become
distributed throughout the aqueous medium as tiny dispersed bubbles and to
permit a major portion of it to dissolve in the aqueous medium. Desirably,
the second volume of hydrogen and subsequent volumes of hydrogen
introduced along the elongated reaction zone are introduced after about
50% of the previously introduced hydrogen has been reacted with oxygen and
preferably after at least 75% of the previously introduced hydrogen has
been reacted.
After the multi-pass reaction, stream 64 flows from pipeline reactor 26. In
the event the off-gas from the reactor is in the flammable range, a
diluent gas 66 can be added to stream 64. An example of a diluent gas
useful for practice of the invention is nitrogen. It has been found that
air can be used in place of nitrogen. While calculations with respect to
the mixture in the reactor vent must be made, it is possible to achieve
substantial economies by using air as the inerting gas rather than pure
nitrogen.
A pressure letdown valve 68 can be used before gas-liquid separator 70 for
reducing the pressure of the inlet mixture 69 to gas-liquid separator 70.
Gas liquid separator 70 separates liquid 72 from gas 74. Gas 74 containing
unreacted oxygen, possibly nitrogen and some unreacted hydrogen from
separator 70 can be recycled with recycled gas compressor 78 and can be
injected at point 75 into liquid stream 24. This provides for safer
operation as discussed above. Alternatively, separated gas 74 can be
purged with valve 76. It will be appreciated that a gas liquid separator
useful for practice of the invention is known in the art. Stream 72 can be
received at additional pipeline reactors 26 for connecting the reactors in
series before gas liquid separator 70.
Separated liquid 72 containing the hydrogen peroxide product in the aqueous
solution of catalyst and acid is passed to a filter 80 for recovering the
catalyst as filter cake 82 or the catalyst may be recovered in a
centrifuge or cyclone. Filter cake 82 can be added to tank 16 for
recycling the catalyst. Filtrate 84 includes the hydrogen peroxide product
and the aqueous acid water solution. Filtrate 84 is received at ion
exchange apparatus 86 for removing the acid from the filtrate.
Hydrogen peroxide product 88 from ion exchange apparatus 86 can be directly
used as a hydrogen peroxide product. Alternatively, hydrogen peroxide
product 88 can be received at column 90 for concentrating the hydrogen
peroxide product 88 in order to produce a concentrated hydrogen peroxide
product 94. Column 90 can be an evaporation or distillation column. Water
92 removed from column 90 can be recycled into water stream 12 as make-up
water.
The concentration of hydrogen peroxide product 82 produced by pipeline
reactor 26 depends on the number of injections of hydrogen and oxygen in
the passes of pipeline reactor 26. Preferably, hydrogen peroxide product
82 has a concentration in the range of about 1% to about 30% of hydrogen
peroxide in solution. Preferably, hydrogen peroxide product 94 has up to
70% concentration.
The invention has the advantage of providing an economical and safe process
for producing hydrogen peroxide. The process does not specifically inject
an inert gas or chemical agent within the reactor, thereby reducing costs.
The entire regime of the pipeline reactor comprises a dispersed bubbly
regime in a rapidly flowing liquid stream for preventing the formation of
an explosive gas phase with the reactor. The entire pipeline is utilized
for the production of the hydrogen peroxide. In addition, the high surface
to volume relationship of the reactor provides inexpensive removal of heat
from the reactor.
EXAMPLE I
Continuous Process
A circulating aqueous stream of a suspended group VIII metal catalyst
deposited on an inert carrier with an acid stabilizer is delivered at a
pressure of 200 atmospheres (3000 psi) to the first of two tubular
reactors operated in series at a flow rate of 195,000 pounds per hour per
reactor in the reactor shown in FIG. 1. The reactor consists of 4"
schedule 160 pipes 100 feet long, each connected together by 180.degree. U
bends. The liquid flow rate has a liquid velocity of 13 feet/second. The
liquid stream is introduced into the reactor at 15.degree. C.
At the reactor inlet 27.2 pounds per hour of hydrogen gas is injected
through a nozzle to form fine individual bubbles in the liquid stream
flowing at 13 feet/second. This produces a bubbly flow regime with a
continuous liquid phase and small evenly dispersed individual bubbles.
Recycled gas from the gas-liquid separator can be injected into the
process fluid. This is followed by the injection of 432 lbs/hr. of oxygen
as finely dispersed bubbles which reacts with the hydrogen to form
hydrogen peroxide. This is followed by repeated injections for each
reactor of first hydrogen and then oxygen to form hydrogen peroxide of
increasing concentration. The heat of reaction is removed by the
circulation of cooled water (or refrigerant) outside the reactor pipes.
After passing through the second reactor, the effluent flows through a
pressure letdown valve before a gas-liquid separator. Nitrogen or other
diluent gas is added to the reactor effluent as needed to assure that the
exit gas from the separator is outside the explosive/flammable limits of
hydrogen and oxygen. This gas can be either recycled to the first reactor
or vented to atmosphere.
The liquid phase is filtered to remove the suspended catalyst slurry so
that it can be resuspended in the aqueous medium. This is done in a mix
tank where the concentration of each ingredient is checked and adjusted as
needed. This includes the acid used as a stabilizer for hydrogen peroxide.
The filtrate from the filter that contains the desired hydrogen peroxide
product passes over an ion exchange or equal agent to remove residual acid
values from the hydrogen peroxide product. This product can then be used
directly or can be concentrated in an evaporator or distillation column to
concentrations up to 70% following conventional practices. A total
production of 100,000,000 pounds per year of hydrogen peroxide can be
produced from these two reactors.
EXAMPLE II
Batch Semicontinuous Process
FIG. 2 illustrates an alternate method of operating the process of the
invention in a batch, semicontinuous fashion. A fresh batch of reaction
medium consisting of a group VIII metal catalyst on an inert support in an
acidic aqueous solution, is .charged through valve 1 to separator 2. The
solution is charged to the reactor via valve 3 and recirculating pump 4.
Once the system is filled, flow of fresh solution is stopped by closing
valve 1. The pressure in the system is increased by closing valve 5.
The velocity of the medium is maintained at 10 feet per second or more.
Recycle gas is injected before the hydrogen at point 12. Hydrogen is
injected at injection system 6. The amount of hydrogen introduced is at or
less than the solubility limit in the flowing medium. Oxygen is introduced
at point 8, at a sufficient distance downstream (pipe length 7) to ensure
the absorption of the bulk of the hydrogen. At full capacity, hydrogen
flow is about 15 pounds per hour and oxygen flow is approximately 250
pounds per hour. Sufficient pipe length 9 is provided downstream of the
oxygen injection to permit the maximum conversion to hydrogen peroxide.
The pipeline is cooled by a coolant on the outside of the pipe to maintain
an operating temperature between 5 and 30.degree. C.
The reactor effluent passes to separator 2 to disengage the gas 10 from the
liquid. If the exit gas is in the flammable region, either air or nitrogen
is injected before the separator. This gas stream can be recycled back to
the reactor. If the exit gas is in flammable region, nitrogen 13 is
injected into the effluent stream.
Pump 4 recirculates the liquid medium until the hydrogen peroxide reaches
its desired concentration, desirably between 4-15% by weight, preferably
5-8%. Gas injection will continue for from one to three hours. The reactor
system, including the separator, pump and piping is then drained. The
system is then refilled with a fresh reactor charge following the
procedure outlined above. This batch semicontinuous procedure produces
from 1,000,000-1,500,000 pounds per year of hydrogen peroxide product.
With smaller or larger diameter pipe of the same length, lower or higher
quantities, respectively, of hydrogen peroxide are produced.
EXAMPLE III
First Modified Batch Semicontinuous Process
The batch semicontinuous process described in Example II can be carried out
in a modified way to reduce both the capital costs and operating costs of
the reaction system. The basic flow diagram of FIG. 2 is used with the
exception that a second reaction medium pump is provided in parallel with
charge pump 4 in order to recirculate the reactor contents at pressure.
This latter feature is accomplished by relocating the pressure let down
valve 5 from the effluent line from the reactor before the separator to
the downstream gas effluent line from the separator 2.
In operation, the operating pressure in the separator remains high
(1,000-4,000 psi) throughout the course of the reaction. Pressure is
maintained by "head" gas above the separator liquid. The gas to be
recycled enters recycle compressor upstream of the pressure letdown valve.
The exit gas in line 10 passes through a pressure letdown valve. By
configuring the process in this way, any residual dissolved gas in the
reactor effluent stays in solution while passing through the separator
because the latter remains at pressure. Thus, it is not necessary to
redissolve gases in the recirculating reactor effluent and both the
separated liquid and unreacted gas need not be repressurized as in Example
II. Configuring the process thusly should reduce the capital and operating
costs of the recirculating pump, the recycle compressor, the separator and
other parts of the process.
EXAMPLE IV
First Modified Continuous Process
A recirculating aqueous stream of a suspended group VIII metal catalyst
deposited on an inert carrier with an acid stabilizer is delivered to the
first of two tubular reactors operated in series in the reactor shown in
FIG. 1. The reactor consists of vertically oriented 4" schedule 160 pipes
100 feet long, each connected together by 180.degree. U bends. The liquid
stream is introduced into the reactor at 15.degree. C.
At the reactor inlet hydrogen gas is injected through a nozzle to form fine
individual bubbles in the liquid stream. This produces a bubbly flow
regime with a continuous liquid phase and small evenly dispersed
individual bubbles. Recycled gas from the gas-liquid separator is injected
into the process fluid. This is followed by the injection of oxygen as
finely dispersed bubbles which reacts with the hydrogen to form hydrogen
peroxide. This is followed by repeated injections for each reactor of
first hydrogen and then oxygen to form hydrogen peroxide of increasing
concentration. The ratio of the volume of liquid medium to the aggregate
volume of hydrogen and oxygen gas may be low but not below the value at
which the process is no longer in the bubbly flow regime. The heat of
reaction is removed by the circulation of cooled water (or refrigerant)
outside the reactor pipes.
After passing through the second reactor, the effluent flows through a
pressure letdown valve before a gas-liquid separator. Air is added to the
reactor effluent as needed to assure that the exit gas from the separator
is outside the explosive/flammable limits of hydrogen and oxygen. The bulk
of this gas can be either recycled to the first reactor or vented to
atmosphere.
The liquid phase is filtered to remove the suspended catalyst slurry so
that it can be resuspended in the aqueous medium. This is done in a mix
tank where the concentration of each ingredient is checked and adjusted as
needed. This includes the acid used as a stabilizer for hydrogen peroxide.
The filtrate from the filter that contains the desired hydrogen peroxide
product passes over an ion exchange or equal agent to remove residual acid
values from the hydrogen peroxide product. This product can then be used
directly or can be concentrated in an evaporator or distillation column to
concentrations up to 70% following conventional practice. A total
production of 100,000,000 pounds per year of hydrogen peroxide can be
produced from these two reactors.
While the invention has been described with reference to the preferred
embodiment, this description is not intended to be limiting. It will be
appreciated by those of ordinary skill in the art that modifications may
be made without departing from the spirit and scope of the invention.
EXAMPLE V
Second Modified Continuous Process
The process carried out in the reactor system shown in FIG. 3 makes
hydrogen peroxide in high yields. The reactor shown in FIG. 3 is identical
to the reactor shown in FIG. 1, with the following exceptions: In FIG. 1
the addition of recycle gas is at inlet 75, downstream of the first
hydrogen inlet and upstream of the first oxygen inlet. In FIG. 3 the
addition of recycle gas is at 75a, upstream of the first hydrogen inlet.
EXAMPLE VI
Second Modified Batch Semicontinuous Process
The process carried out in accordance with the reactor system shown in FIG.
4 makes hydrogen peroxide in high yields. The reactor is identical to the
reactor shown in FIG. 2, with the following exceptions: In FIG. 2 recycle
gas is added into the oxygen supply at inlet 12, forming an oxygen/recycle
gas stream. This stream was added to the liquid reactor flow at an inlet
downstream of the hydrogen inlet. In FIG. 4 the addition of the recycle
gas is at 12a. The recycle gas is not combined with oxygen upstream of the
hydrogen inlet.
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